Allow to set accel sensor orientation

Signed-off-by: Francesco Gazzetta <fgaz@fgaz.me>

apps/Level.py

@@ -77,17 +77,19 @@ class LevelApp():
     def _update(self):
         if not self.prompt:
             draw = wasp.watch.drawable
+            # Clear the old bubble
             draw.fill(None, self.old_xy[0] - 3 + _X_CENTER, self.old_xy[1] - 3 + _Y_CENTER, 6, 6)
             # draw guide lines
             draw.line(0, _Y_CENTER, _X_MAX, _Y_CENTER, color = wasp.system.theme('mid'))
             draw.line(_X_CENTER, 0, _X_CENTER, _Y_MAX, color = wasp.system.theme('mid'))
-            # We save x as y and -y as x because we use the screen's coordinate
-            # system.
-            # We also clamp and scale the values down a bit to make them fit better,
-            # and apply the calibration
-            (new_y, new_x, _) = watch.accel.accel_xyz()
+            (new_x, new_y, _) = watch.accel.accel_xyz()
+            # We clamp and scale the values down a bit to make them fit better,
+            # and apply the calibration.
+            # The scaling factor is negative because when gravity pulls in one
+            # direction we want the bubble to go the other direction.
             new_x = min(_X_CENTER, max(-_X_CENTER, (new_x-self.calibration[0])//-3))
-            new_y = min(_Y_CENTER, max(-_Y_CENTER, (new_y-self.calibration[1])//3))
+            new_y = min(_Y_CENTER, max(-_Y_CENTER, (new_y-self.calibration[1])//-3))
+            # Draw the new bubble
             draw.fill(wasp.system.theme('bright'), new_x - 3 + _X_CENTER, new_y - 3 + _Y_CENTER, 6, 6)
             self.old_xy = (new_x, new_y)
 
@@ -99,7 +101,7 @@ class LevelApp():
         if self.prompt:
             # Handle buttons
             if self.calibrate.touch(event):
-                (y, x, _) = watch.accel.accel_xyz()
+                (x, y, _) = watch.accel.accel_xyz()
                 self.calibration = (x, y)
             if self.reset.touch(event):
                 self.calibration = (0,0)

wasp/drivers/bma421.py

@@ -8,17 +8,33 @@
 import bma42x
 import time
 
+# Sensor orientation definition.
+# The 6 most significant bits define the indexes of the x, y, and z values
+# in the acceleration tuple returned by the sensor, while the 3 least
+# significant bits define their sign (1 = keep original sign, 0 = negate).
+#
+#         Z index ─────────────────┐
+#         Y index ───────────────┐ │
+#         X index ─────────────┐ │ │
+#                              ├┐├┐├┐
+_DEFAULT_ORIENTATION = const(0b010010101)
+#          1 = keep, 0 = negate      │││
+#          X sign ───────────────────┘││
+#          Y sign ────────────────────┘│
+#          Z sign ─────────────────────┘
+
 class BMA421:
     """BMA421 driver
 
     .. automethod:: __init__
     """
-    def __init__(self, i2c):
+    def __init__(self, i2c, orientation=_DEFAULT_ORIENTATION):
         """Configure the driver.
 
         :param machine.I2C i2c: I2C bus used to access the sensor.
         """
         self._dev = bma42x.BMA42X(i2c)
+        self._orientation = orientation
 
     def reset(self):
         """Reset and reinitialize the sensor."""
@@ -52,4 +68,8 @@ class BMA421:
 
     def accel_xyz(self):
         """Return a triple with acceleration values"""
-        return self._dev.read_accel_xyz()
+        raw = self._dev.read_accel_xyz()
+        x = raw[self._orientation >> 7 & 0b11] * ((self._orientation >> 1 & 0b10) - 1)
+        y = raw[self._orientation >> 5 & 0b11] * ((self._orientation      & 0b10) - 1)
+        z = raw[self._orientation >> 3 & 0b11] * ((self._orientation << 1 & 0b10) - 1)
+        return (x, y, z)